The present invention relates to an apparatus in a power train including an engine and an automatic transmission, for reducing a shift shock of the automatic transmission by a torque down control of the engine.
An automatic transmission varies in input rotation at gearshift due to a change of gear ratio, which variation in input rotation causes an inertia torque which is causative of a shift shock.
More specifically, in case, for example, the automatic transmission is shifted from a lower gear ratio to a higher gear ratio, the transmission input rotation is decreased by an amount corresponding to the difference between the gear ratios, which decrease in input rotation causes a release of torque for inertia (inertia torque) which in turn causes a shift shock.
As a countermeasure for a shift shock of a power train which occurs due to such a theory is used in many cases a technique for decreasing an engine torque thereby offsetting the inertia torque (torque down control).
Since during an inertia phase in which an effective gear ratio that is a ratio between input and output rotations of the automatic transmission is changing from a before-shift gear ratio to an after-shift gear ratio, a variation in the input rotation occurs due to a change of the gear ratio and causes an inertia torque that is causative of a shift shock, it is generally practiced to execute a torque down of the engine (torque down control) during the inertia phase.
In the meantime, since the toque down of the engine will start after the start of the inertia phase if started after detection of the start of the inertia phase, which start of the inertia phase is detected through detection of the start of a change of an effective gear ratio from a before-shift gear ratio to an after-shift gear ratio, a shift shock due to a release of toque at the initial stage of the inertia phase cannot be avoided.
Thus, as described in Unexamined Japanese Patent Publication No. 07-139381, it has heretofore been proposed an apparatus for reducing a shift shock of a power train, which is adapted to execute, according to the necessity, a toque down (herein referred to as pre-torque down) that causes an engine torque to start decreasing gradually before the start of the inertia phase, i.e., during a torque phase, specifically, from the time after the issuing of a gearshift instruction and before the start of the inertia phase and thereafter a large decrease in toque of the engine is executed during the inertia phase.